A robot has built a firm position as an apparatus for conveyance or assembly for savings in labor and person, and has been frequently used in the field of manufacturing industries such as an automobile industry, an electrical appliance industry or a semiconductor industry. Particularly, a technique of brake unlocking is effective in reducing packing volume by moving an arm of a robot to an attitude at the time of conveyance, and also is effective in a return operation of the case that control became impossible by movement beyond a stroke, and is a basic technique of the robot.
FIG. 16 is a block diagram of a conventional industrial robot control apparatus for unlocking a brake and being shown in JP-A-11-179691, and FIG. 17 is a flowchart of brake control, and FIG. 18 is a state diagram showing a brake action.
A configuration will be described below. In the drawings, numeral 1 is a robot body which has a set of a motor 11, a position detector 12 and a brake 13 per one joint. Numeral 2 is a control apparatus which drives and controls the robot body 1 by an action program, and has a central processing unit 21, a servo control part 23, a servo amplifier part 24, a brake control part 25 and a brake driving part 26. Numeral 3 is a manual operation apparatus and an operator gives a command necessary for robot control.
The central processing unit 21 in the control apparatus 2 is a part for generating commands of position control or various functions of the robot body 1 based on a control program. The servo control part 23, the servo amplifier part 24 and the motor 11 form a servo control system. At the time of control of a servo system, a command about movement or stop is given to the servo control part 23 and its command is further passed to the servo amplifier part 24 and turning force for driving a robot arm (not shown) is finally generated in the motor 11 and when a movement command is not given, the turning force balances with its own weight of the robot arm to make a stop. Also, when the movement command is given, it is constructed so that turning force larger than force for offsetting its own weight of the robot arm is generated and the robot arm moves.
Also, the position detector 12 is mounted in the motor 11. The position detector 12 recognizes a servo control position of the robot arm, and is actually constructed so that a rotational angle of the motor 11 is detected and an output signal of the rotational angle is fed back to the servo control part 23 and the servo amplifier part 24 and as a result of that, the robot arm always maintains a position command value from the operation part 3. The brake 13 is mounted integrally with a shaft of the motor 11 or between the shaft and the robot arm. Numeral 27 is a brake unlocking time setting part, and numeral 28 is a brake locking time setting part. The brake unlocking time setting part 27 and the brake locking time setting part 28 are constructed so as to be allocated to memory (not shown) of the central processing unit 21 as parameters of the robot control apparatus and be able to be changed from the manual operation apparatus 3 etc. by an operator. The brake driving part 26 performs driving so as to unlock or lock the brake 13 actually by an output signal from the brake control part 25. It is constructed so that an unlocking command of the brake 13 is generated by pushing an unlocking operation switch (not shown) present in the manual operation apparatus 3.
Next, an action will be described. First, the central processing unit 21 decides a working state of an unlocking operation switch of the manual operation apparatus 3 in step S71. When the unlocking operation switch of a brake unlocking command is “ON”, the action proceeds to step S72 and the central processing unit 21 performs control stop processing of a servo system. That is, a locking action of the brake 13 is performed and a signal output to the servo control part 23, the servo amplifier part 24 and the motor 11 is stopped and a robot arm stops by the brake 13. Next, in step S73, the brake control part 25 reads unlocking time data from the brake unlocking time setting part 27, and outputs a signal to the brake driving part 26 so as to unlock the brake 13 for only time according to the unlocking time data. After a lapse of the unlocking time, it proceeds to step S74, and the brake control part 25 reads locking time data from the brake locking time setting part 28, and outputs a signal to the brake driving part 26 so as to lock the brake 13 for only time according to the locking time data. After a lapse of the locking time, it returns to decision on the working state of the unlocking operation switch of step S71. As a result of this, as shown in FIG. 18, while an operator continues to push the unlocking operation switch of the manual operation apparatus 3, unlocking and locking actions of the brake 13 are performed based on the data for the respective time.
Also, when the unlocking operation switch is not pushed (OFF), it proceeds to step S75, and processing for deciding whether or not control of the servo system is being exercised is performed and thereafter, it returns to step S71. As a result of that, during the control of the servo system, an unlocked state of the brake 13 continues always. Also, in the case of a state other than in the servo control action in step S75, processing for locking the brake 13 in step S77 is performed and thereafter, it returns to decision on the working state of the unlocking operation switch of step S71.
As described above, the conventional robot presets brake unlocking time and locking time and repeats a sequence of locking and unlocking of the brake 13 based on this setting time, so that a movement speed of an arm at the time of brake unlocking greatly depends on weight, an attitude and a load of the arm.
For example, when the center of gravity in which the weight or the load, etc. of the arm are combined is located in a substantially horizontal position viewed from the center of rotation of a joint in which a brake attempts to be opened, the moment about the joint becomes maximum and as a result of that, rotational acceleration also becomes maximum and the movement speed of the arm increases suddenly at the time of unlocking the brake.
Also, when the center of gravity is located in a substantially vertical position viewed from the center of rotation of the joint, the moment about the joint becomes close to zero and there may be a state in which the arm does not start to move unless an operator applies force due to the presence of friction of a joint part even at the time of unlocking the brake.
In the conventional robot thus, the arm movement speed in the case of unlocking the brake varies suddenly due to weight, an attitude and a load condition, etc. of the arm, so that it was necessary to adjust time setting of locking and unlocking of the brake while the operator monitors movement of the arm
Also, in a state in which the arm does not move in the case of unlocking the brake, an operation in which the operator applies force to the arm by hand, etc. was necessary and further it was necessary to perform an operation of the unlocking operation switch and it was difficult to do work alone.